1. Field of the Invention
The present invention relates to a butterfly valve having a water-filling function, and to a technology of a valve for supplying a constant amount of fluid when a pipe is filled with water.
2. Description of the Related Art
In the prior art, in the initial filling of water or refilling of water when laying a pipe, the pipe was often damaged by a water hammer or the like if the water was filled up with water suddenly. Therefore, a butterfly valve provided in the middle of the pipe was opened to a small degree to fill a downstream pipe line with water by supplying a small amount of water.
However, with a general butterfly valve, it was difficult to control the quantity of water flow by opening the valve to a small degree, thus a constant amount of water could not be supplied. Therefore, it was difficult to previously compute required time between the start of water filling and when the pipe became full of water.
As a measure of such problems, there is a configuration, as shown in FIG. 4, in which a main pipe 2 having a butterfly valve 1 is provided with a sub-pipe 3 for water filling, and a sub-pipe valve 4 is provided in the middle of the sub-pipe 3. One end of the sub-pipe 3 is connected to the main pipe 2 positioned upstream of the butterfly valve 1, and the other end of the sub-pipe 3 is connected to the main pipe 2 positioned downstream of the butterfly valve 1.
According to such structure, in the filling of water, the butterfly valve 1 is closed and the sub-pipe valve 4 is opened, whereby the fluid inside the main pipe 2 flows from the upstream side of the butterfly valve 1 to the downstream side of the butterfly valve 1 via the sub-pipe 3 to fill a downstream pipe line in small amounts. It should be noted that usually the diameter of the sub-pipe 3 is set to be ⅕ of the diameter of the main pipe 2, thus the cross-section of the flow channel of the sub-pipe 3 is 1/25 of the cross-section of the flow channel of the main pipe 2, according to a standard and the like.
However, in the configuration in which the sub-pipe 3 and the sub-pipe valve 4 are provided as described above, there was a problem that such configuration takes up a large space for setting up pipes. As a measure of such problems, a butterfly valve 10 with a water-filling function as shown in FIG. 5 through FIG. 8 is considered to be used.
Specifically, as shown in FIG. 8, an upstream pipe 21 and a downstream pipe 22 are connected to both sides of a valve casing 11 of the butterfly valve 10. Moreover, as shown in FIG. 5, in the valve casing 11 a valve body 12 is rotatably disposed around a shaft center 13a of a valve rod 13. An annular valve casing seal 14 is disposed on an inner periphery of the valve casing 11. A rim of the valve body 12 contacts with and slides on the valve casing seal 14 in a completely closed state S of the valve body 12. The valve body 12 comprises a disk tail portion 15a, 15b at each of a right and left pair of valve body pieces 12a, 12b that have the valve rod 13 therebetween. The pair of disk tail portions 15a, 15b are disposed at the back side of the valve body 12 in a rotation direction C when opening the valve body 12.
Each of the both disk tail portions 15a, 15b stands on the face of a flat portion of the valve body 12, and has an outer periphery that is spherically curved so as to contact with and slide on the valve casing seal 14. A water flow hole 17 is formed on each of the both disk tail portion 15a, 15b. One end of the water flow hole 17 is opened to the outer peripheries of the disk tail portions 15a, 15b, and the other end of same is opened to the other sides of the disk tail portions 15a, 15b, that is, the back side of the valve body 12 when the valve body 12 is operated to be opened.
As shown in FIG. 6, in the disk tail portion 15a provided in the valve body piece 12a which is turned toward the upstream side in the opening operation, the water flow hole 17 forms an inflow port 17a at the opening on the outer periphery of the disk tail portion 15a, and an outlet port 17b at the opening on the back side of the valve body 12. Furthermore, in the disk tail portion 15b provided in the valve body piece 12b which is turned toward the downstream in the opening operation, the water flow hole 17 forms an inflow port 17c at the opening on the back side of the valve body 12, and an outlet port 17d at the opening on the outer periphery of the disk tail portion 15b. As shown in FIG. 7, the opening of the water flow hole 17 has an oblong shape so as to follow the circumferential direction of the valve body 12. It should be noted that the total opening area of the openings of the water flow holes 17 is set to be the same as the cross-section of the flow channel of the sub-pipe 3 shown in FIG. 4. Specifically, the total opening area of the water flow holes is 1/25 of the pipes 21, 22 connected to the butterfly valve 10.
It should be noted that the valve rod 13 is rotated by a switching device including a reducer, and a handle or a motor.
According to the above description, the valve body 12 is in a completely closed state in the beginning of the operation for water filling, as shown in FIG. 5, and the butterfly valve 10 is opened to a small degree to fill the downstream pipe with water in small amounts in order to prevent the pipe from being damaged by rapid filling of water. Specifically, as shown in FIG. 6, the valve body 12 is opened to a small degree (approximately 15 through 20%) by the opening operation. Accordingly, the water flow holes 17 are opened completely in a state in which the outer peripheries of the disk tail portions 15a, 15b contact with and slide on the valve casing seals 14.
By opening the valve body 12 to a small degree and opening the water flow holes 17 completely, an upstream region and a downstream region in the valve casing 11 which is separated by the valve body 12 are communicated with the disk tail portions 15a, 15b only via the water flow holes 17. Consequently, the water flowing from the upstream pipe 21 into the valve casing 11 is guided to the downstream pipe 22 via the water flow holes 17.
In this case, the amount of water flowing through the water flow holes 17 is previously set so as to correspond to the shape of the flow channel such as the cross-section of the flow channel of the water flow hole 17, thus the downstream pipe 22 can be filled at a constant flow rate, and required time from the start of water filling till the pipe becomes full of water can be computed beforehand.
It should be noted that a graph A that is drawn with a chain double-dashed line in FIG. 2 shows the relationship between the opening degree (%) of the valve body 12 of the conventional butterfly valve with a water-filling function 10 and loss factor. When the opening degree is 20% or less the outer peripheries of the disk tail portions 15a, 15b contact with and slide on the valve casing seals 14, and when the opening degree is between 15 and 20% the water flow holes 17 are opened completely. According to the above description, the graph A slopes downward as the opening degree of the valve body 12 rises, whereby the loss factor decreases. However, when the opening degree is between 15 and 20%, the water flow holes 17 are opened completely, thus a steady region Ra, which indicates that the loss factor is a constant value, appears. It should be noted that in the case of water filling as described above, the opening degree is 20% or less.
Here, the loss factor fv can be obtained in the following equation 1 in which the water filling velocity in the upstream pipe 21 in the butterfly valve 10 when performing filling of water from the water flow hole 17 is V (m/s), the pressure head upstream of the butterfly valve 10 is H (m), and the acceleration of gravity is g (=9.8 m/s2).fv=H×2×g/V2  Equation 1
For example, when the butterfly valve 10 is provided in a water pipe line, the water filling velocity V when filling water is performed is generally set to 0.5 m/s with safety in mind. The upstream pressure head H is set to 100 m (=9.8×105Pa) based on standard hydraulic conditions of water pipe lines. The loss factor fv obtained by the above equation 1 in this condition is approximately 8000 (to be precise, fv=7845). Therefore, in order to perform filling of water at a water filling velocity V of 0.5 m/s, it is necessary to maintain the opening degree of the valve body 12 at approximately 10% according to the graph A of FIG. 2.
However, the opening degree of the valve body 12 easily fluctuates in accordance with backlashing of the switching device or the like. If the opening degree of the valve body 12 slightly fluctuates from the 10%, the loss factor fv largely changes in accordance with this fluctuation, thus the water filling velocity V changes from 0.5 m/s, whereby the amount of water filling also fluctuates. Therefore, there is a problem that the required time between the start of water filling and when the pipe becomes full of water differs from a previously calculated required time.
The present invention is, therefore, to provide a butterfly valve having a water-filling function which can minimize the difference between an actual required time from the start of water filling till a pipe becomes full of water, and a previously calculated required time.